DIY Mic Pre Kits, Lunchbox Mic Preamp Kits, Power Supply Kits

Hi -- I assembled one 2448 PS and fried the board in one place, and instead of trying to work around it I ordered a second 2448. Second one should be easy, right? All the parts are supplied, locations are clearly marked...

Anyway, It's all put together and I've got LED 2 lit but not LED 1. I reversed the connection then replaced the LED, still the same status.

WHen I measure voltage, I've got 21v for phantom, +6.9v and -1.2v. All the solder joints look shiny, and I don't see any shorting pins or scraps of solder on the back of the board.

What are the likely suspects for a problem like this? R1, the furthest right 3.5k resistor, was a little mangled in installation. I could replace that, but after reading other issues around here I don't know if that's the source of the problem.

Any thoughts? What are the likely suspects for this issue?

Is your power transformer wired correctly?

What AC voltages are you feeding the PSU kit?

Have you adjusted the trimmers? There are (3) voltage trimmers.

All resistors should be properly soldered, otherwise, that could cause problems for you not reaching the correct voltage.

Your -1.2V reading is suspect of an open/cold solder joint in that section.

Did you swap the LM317 and LM3317 voltage regulators? This is a common mistake by builders.

Can you send a photo of your soldering job? Photo of bottom of PCB.

_________________

Photos at bottom

The regulators are in the right place -- triple checked that this time around since that was the start of the destruction of the first PCB. Voltage is coming from the FiveFish transformer kit, and it looks like everything is hooked up correctly. I'll measure voltage tomorrow evening, have to make this quick.

Tomorrow maybe I'll go back over the resistors in that area.

You need to cut those long leads on the voltage regulators.

Need more solder on the 1000uf 80V snap-in caps.

Let me know the AC voltage readings you're getting.

And the DC voltage reading you're getting across C1, C8, C9, and C18.

Make sure none of the diodes are inserted backwards. D1 to D6.

_________________

Haven't snipped the regulators yet, or added solder to the big capacitors.

Putting the meter's Neg lead on the CT and Pos on both the AC1 and AC2 connections, with the meter at a 000-999 v and "Auto range", I get 0 V. With just the POS lead on AC1 or AC2 I get 12.4 v on either one.

Let me know the AC voltage readings you're getting.

And the DC voltage reading you're getting across C1, C8, C9, and C18.

C8 and C9 = 12.5 V

C1 and C18 = 12.2 V

Diodes are consistently positioned with the white band at top (toward the regulators).

Next: More solder on C1 and C18, resoldering all the resistors, I suppose. And snipping the long legs off of the regulators.

Thanks!

Make sure none of the diodes are inserted backwards. D1 to D6.[/quote]

Forget auto-range. Is your meter set correctly to AC reading?

The transformer you got from me (I'm assuming you're using my transformer) is 18VAC output per winding.

Did you wire the transformer primaries correctly? Are you on 110V or 220V system? Did you follow the wiring for your respective voltage?

I hate to ask this obvious question but this has happened more than twice already from previous customers.... IS YOUR VOLTMETER WORKING CORRECTLY?

_________________

I'm working on this a bit at a time, when I have a half hour here or there.

I'm on 110v, using the fivefish transformer kit, and the AC wiring matches the instructions: Brown/grey are paired and run to the switch with the fuse between the switch and the AC receptacle. Blue/violet paired and go to the receptacle, with the middle receptacle pin grounded to the case.

On the other side of the transformer, red/orange go to CT and are soldered together on the back of the PCB. Black goes to AC1 and yellow goes to AC2.

After clipping long component legs on the back of the PCB, I re-applied solder to the most imperfect-looking connections.

The resistors all give the correct reading in ohms (read off the component legs on the back of the PCB.)

When I switch the lunchbox on I still only have one of the two LED's lighting. LED 1 (closest to the 48v/+15/-15 pads) isn't lighting.

C9 and C8 now read -27v

C18 reads -21v

C1 reads -55v

I'm pretty sure the meter works OK -- if I plug in a wall-wart power supply that's marked 5v AC output, it reads 5v when tested.

Any more clues in this information?

The other LED was probably inserted backwards that's why it's not lighting up.

If you're now getting these readings, these look more in line with normal. I think your PSU is working correctly. Your polarity's may be off (but that's maybe you just have the negative lead on your tester in the wrong location).

Adjust the three trimmers to adjust for 48V, +18V and -18V.

_________________

I'm still in the place I started -- trimmer resistors have no effect with 6-8 half turns of the screw. Phantom hovers at 21, the other voltages are +6.9v, -1.2v.

One LED lights, and if I swap polarity, still no light. If I put the LED that was connected to LED 1 (and lit) on LED 2, it does not light. That may be unclear -- whichever LED is attached to the LED 2 point works, whichever LED is attached to LED 1 does not.

I will go over solder points again tomorrow, but I'm wondering what Fivefish's charge is for going over operator-error induced tech issues?

I'm confused. You said you got the following voltages:



but then you said



This shows that you have cold solder joints around the trimmers and resistors. The input voltage going in is fine... but the output voltages you're getting are not correct. You probably have open connections or shorts in your soldering job.

Send it back if you want. I charge $45 labor + shipping. I don't know the condition of your assembly but if it's bad, I'll just throw it out and build you a new unit from scratch.

_________________